Ion generator

ABSTRACT

In an ion generator comprising a discharge needle  2 , an opposed electrode  3  opposite the discharge needle  2  and an AC high voltage power source  4 , for generating positive and negative air ions by giving rise to a corona discharge when a high voltage is applied by the AC high voltage power source  4  between the discharge needle  2  and the opposed electrode  3 , the AC high voltage power source  4  comprises a high frequency oscillator  7  and a piezoelectric transformer  9 , and outputs a high frequency voltage. An insulator  5  is placed intervening between the high voltage output line  4   a  of the AC high voltage power source  4  and the discharge needle  2  to capacitance-couple them, and the discharge needle  2  is enabled to discharge electricity. Preferably, the surface of the opposed electrode  3  should be covered with an insulator. This enables the balance between positive and negative air ions and its stability to be improved while reducing the hardware configuration in size and weight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national phase application of PCTInternational Patent Application No. PCT/JP04/08016 filed on Jun. 2,2004 and claiming the benefit of priority of Japanese Patent ApplicationNo. 2003-160873 filed on Jun. 5, 2003.

TECHNICAL FIELD

The present invention relates to an ion generator which generates bycorona discharge positive and negative air ions suitable forneutralizing the static electricity of and deelectrifying a chargedobject.

BACKGROUND ART

There is already known an ion generator which applies a high voltagefrom an AC high voltage source of the commercial frequency (50 or 60 Hz)between a discharge needle and an opposed electrode, generates a coronadischarge from the discharge needle and ionizes air by that coronadischarge (see Japanese Patent Application Laid-Open No. 8-288094 forinstance).

In an ion generator of this kind, positively charged air ions andnegatively charged air ions are alternately generated by alternatelyapplying an AC voltage to the discharge needle. And the ion generator ofthis kind, as it can neutralize the electric charges (staticelectricity) accumulated on the charged object with the generatedpositive and negative air ions, is generally used as a deelectrifyingdevice for clearing charged objects of static electricity.

Further, a consideration is given in the ion generator of this kind tothe short-circuiting current which may be generated when a human body orthe like comes into contact with the discharge needle, and theshort-circuiting current is restrained by capacitance-coupling thedischarge needle with the high voltage output line from the AC highvoltage source. In the ion generator in this case, at the time ofgeneration of a corona discharge (at the time of discharge by thedischarge needle) the impedance of the coupled capacitance of thedischarge needle causes the discharge needle to reduce the voltage ofthe high voltage output line. In order to generate a corona discharge atthe commercial frequency, the discharge needle requires a voltage ofabout 4 kV at its tip. For this reason, this ion generator uses an AChigh voltage power source which outputs a high voltage, augmented with acompensation for the voltage drop due to the impedance of the coupledcapacitance of the discharge needle, to the high voltage output line.

It is difficult here for the discharge needle to have a very largecoupled capacitance because of structural constraints and the need tosecure the effect to restrain the short-circuiting current, and thecapacitance can be at most 10 pF or so for practical purposes. As aresult, the voltage drop attributable to this coupled capacitanceincreases. In a case in which coupled capacitance is 10 pF and thecommercial frequency is 50 Hz, the voltage drop will reach about 1.6 kV.Incidentally, the discharge current of the discharge needle is about 3μA to 10 μA, and the above-mentioned level of the voltage drop is whatmatches a discharge current of 5 μA. Therefore, in order to compensatefor this voltage drop, the conventional ion generator uses as theboosting transformer for the AC high voltage power source a wound-wiretransformer having a sufficient number of windings to generate a highvoltage of about 6 to 9 kV. However, since a wound-wire transformer isrelatively large and heavy, this involves a problem of difficulty tomake the ion generator compact and light.

On the other hand, there is also known an ion generator using apiezoelectric transformer, which is more compact and lighter than awound-wire transformer and an AC high voltage power source of a highfrequency of a few tens of kHz instead of the commercial frequency (seeJapanese Patent Application Laid-Open No. 2003-22897 for instance). TheAC high voltage power source of this ion generator generates a highfrequency AC high voltage by providing a high frequency signal of a fewtens of kHz from a high frequency oscillator to the piezoelectricelement of the piezoelectric transformer. An ion generator using such ahigh frequency power source, compared with what uses a power source ofthe commercial frequency, can improve the ion balance of air ions (thebalance between the quantity of positive ions and that of negativeions), and moreover can reduce the voltage needed for generating acorona discharge from the tip of the discharge needle to about 1.8 kV.

The output voltage of the high frequency power source using thispiezoelectric transformer is at most about 2 to 3 kV because of thecharacteristics of the piezoelectric transformer, and this outputvoltage is close to the voltage (about 1.8 V) needed by the dischargeneedle to generate a corona discharge by using that high frequency powersource. Therefore, in order to secure the voltage of the dischargeneedle at a level allowing the generation of a corona discharge, thevoltage drop from the high frequency power source to the dischargeneedle has to be kept sufficiently small. As the current a piezoelectrictransformer can output is generally small (at most about 100 μA), theshort-circuiting current can be kept sufficiently small without havingto capacitance-couple the discharge needle with the high voltage outputline.

On account of these circumstances, in the conventional ion generatorusing a high frequency power source, the high voltage output line isdirectly connected to the discharge needle (the discharge needle is notcapacitance-coupled with the high voltage output line) so that nosuperfluous voltage drop may occur between the high voltage output lineof the high frequency power source and the discharge needle.

Incidentally, the requirement for neutralizing charged objects whereverpracticable on the production lines of precision semiconductor devicesand elsewhere has become even more stringent in recent years. In meetingthis requirement, an ion generator using a high frequency power sourceis more advantageous than an ion generator using a commercial frequencypower source. However, in the conventional ion generator using a highfrequency power source, the ion balance is often destabilized, and therequirement cannot be always fully satisfied.

An object of the present invention, attempted in view of thesebackground circumstances, is to provide an ion generator reduced in thesize and weight of hardware configuration and capable of improving thebalance between positive and negative air ions and its stability.

DISCLOSURE OF THE INVENTION

The invention, intended to achieve the foregoing object, relates to anion generator comprising at least one discharge needle, an opposedelectrode opposite the discharge needle, and an AC high voltage powersource for applying a high voltage between the discharge needle and theopposed electrode, for generating positive and negative air ions bygiving rise to a corona discharge when a high voltage is applied betweenthe discharge needle and the opposed electrode by the AC high voltagepower source.

To achieve the foregoing object, the inventors pertaining to the presentapplication conducted various studies and experiments. As a result, theinventors found that, in an ion generator provided with a high frequencyAC power source equipped with a piezoelectric transformer, even if thedischarge needle was capacitance-coupled with the high voltage outputline of the high frequency AC power source, an AC corona discharge couldbe satisfactorily generated from the discharge needle while sufficientlyreducing the drop of the voltage from the high voltage output line fromthe high frequency AC power source to the discharge needle and that atthe same time the capacitance coupling could serve to balance thequantities of the positive and negative air ions and to stabilize thatbalance compared with the conventional high frequency ion generator,thereby improving the ion balance.

Therefore, the present invention uses an AC high voltage power sourcecomprising a high frequency oscillator and a piezoelectric transformerand outputs a high frequency voltage, and an insulator is placed tointervene between the high-voltage output line of the AC high-voltagepower source and the discharge needle to enable the discharge needle toaccomplish discharging.

According to the invention configured in this way, the interveningpresence of the insulator between the high voltage output line and thedischarge needle results in capacitance coupling of the high voltageoutput line and the discharge needle by the insulator. And by using whatoutputs a high frequency voltage as the AC high voltage power source andcapacitance-coupling the high voltage output line and the dischargeneedle with the insulator, the quantities of positive and negative airions can be balanced and the balance can be stabilized, namely the ionbalance can be improved, compared with the conventional ion generatorwhich uses the commercial frequency voltage or the conventional highfrequency type ion generator in which the high voltage output line andthe discharge needle are directly connected. In this case, the ionbalance can be improved while setting the capacitance between thedischarge needle and the high voltage output line to such a value thatthe voltage drop due to that capacitance would be sufficiently reduced.Since the AC high-voltage power source is a high frequency power sourceprovided with a high frequency oscillator and a piezoelectrictransformer, the hardware can be reduced in size and weight comparedwith a commercial frequency high voltage power source equipped with awound-wire transformer. Furthermore, as it uses an AC high voltage powersource provided with a piezo electric transformer, the short-circuitingcurrent of the discharge needle can be sufficiently restrained.

The form of the intervening presence conceivable here of the insulatorbetween the discharge needle and the AC high voltage power source (thestructural form of coupling capacitance) may be one of the following twoforms for instance.

In a first mode, the high voltage output line of the AC high voltagepower source is covered with an insulating tube as the insulator, thehigh voltage output line covered with this insulating tube is insertedinto a current collector ring formed of a conductor in a state in whichthe high voltage output line is insulated from the current collectorring by the insulating tube, and conduction is established between thesurface of the current collector ring into which the high voltage outputline is inserted and the discharge needle.

In the first mode, since the high voltage output line and the dischargeneedle are capacitance-coupled by the insulating tube covering the highvoltage output line and the current collector ring into which these areinserted, the structure of the coupling capacitance can be simplified.

In a second form, conduction of the discharge needle is established witha first conductor pattern formed on one face of a plate-shaped insulatoras the insulator, and conduction of the high voltage output line isestablished with to a second conductor pattern formed on the other faceof the plate-shaped insulator in a position matching the first conductorpattern.

In the second mode, a parallel plate condenser functioning with aplate-shaped insulator serving as a dielectric and a conductor patterndisposed on each face of the insulator serving as an electrode isformed, and the parallel plate condenser capacitance-couples thedischarge needle and the high voltage output line. In this case, sinceeach conductor pattern can be readily formed of, for instance, a metalmember melt-fastened onto a face of the plate-shaped insulator or acircuit pattern (pattern of a conductive thin film layer) printed on aface of the plate-shaped insulator, capacitance coupling of thedischarge needle and the high voltage output line can be accomplished ina low cost simple structure by using a circuit board or the like as theplate-shaped insulator.

Where a plate-shaped insulating member is to be used as in the foregoingcase and a plurality of discharge needles of the above-described kindare provided, the first conductor pattern comprises a plurality ofpartial conductors establishing conduction of the discharge needles withone another arranged on one face of the plate-shaped insulator in apattern in which the partial conductors are insulated from one anotherby said plate-shaped insulator and matched with the arrangement of theplurality of discharge needles, and the second conductor patterncomprises a plurality of partial conductors opposite the partialconductors of the first conductor pattern via the plate-shaped insulatorand a partial conductor linking the plurality of partial conductors inconduction with one another.

According to this, the discharge needles and the high voltage outputline are capacitance-coupled partially (in the part of the plate-shapedinsulator) between the partial conductors of the first conductor patternmatching the discharge needles and the partial conductors of the secondconductor pattern opposed to those partial conductors. In this case, thehigh-voltage output line is capacitance-coupled with the dischargeneedles while establishing conduction to only part of the secondconductor pattern. It is also possible to use only one plate-shapedinsulator, instead of providing one plate-shaped insulator for everydischarge needle, and capacitance-couple each discharge needle to thehigh voltage output line. Therefore, where a plurality of dischargeneedles are to be disposed, each of the discharge needles can becapacitance-coupled with the high voltage output line in a compact andsimple structure.

Where a plurality of discharge needles and a plate-shaped insulator areprovided as described above, the discharge needles are arranged in thefollowing way for instance. Thus, the plurality of discharge needles,with the base end of each being fixed to the partial conductors of thefirst conductor pattern of the plate-shaped insulator, are laidextending around the plate-shaped insulator in a pattern of arrangementradiating from the plate-shaped insulator. And the opposed electrode iscomposed of an annular conductor so arranged around the plurality ofdischarge needles as to have an axis in a direction substantiallyorthogonal to the axis of each discharge needle.

As this configuration enables the electric fields between the opposedelectrode and the discharge needles to be uniformized for everydischarge needle, it is made possible to restrain fluctuations in thestate of generation of air ions by the discharge needles. Further, onaccount of the presence of the opposed electrode around the plurality ofdischarge needles radially extending from the plate-shaped insulator,when these discharge needles and opposed electrode are to be housed in acase, the plate-shaped insulator is necessarily arranged near thecentral part of the inner space of the case. For this reason, thecapacitance between the second conductor pattern of the plate-shapedinsulator to which a high voltage is applied and the high voltage outputline whose conduction to the pattern or the case can be kept small,thereby to keep small any leak current between the second conductorpattern and the high voltage output line or the case.

Further, according to the present invention described above, preferablythe opposed electrode facing the discharge needles is covered with aninsulator. Since the opposed electrode opposite the discharge needlesare covered with the insulator in this configuration, the insulatorfunctions between the discharge needles and the opposed electrode as acapacitance connected to the opposed electrode. As a result, thequantity of air ions directed from the vicinities of the tip of thedischarge needles toward the opposed electrode is restrained frombecoming predominantly positive or negative, and the ion balance of thepositive and negative air ions that can be discharged can be furtherimproved.

Further, especially where a plurality of radially extending dischargeneedles are provided, preferably the opposite electrode which is theannular conductor is fitted to the outer circumference of a cylindricalinsulator, the cylindrical insulator accommodating therein a pluralityof the discharge needles and the plate-shaped insulator and beingarranged coaxially with the annular conductor, and comprises, within thecylindrical insulator, means of supplying air in the axial directionthereof.

This makes it possible for the cylindrical insulating member to readilyconstitute an insulator to cover the annular opposed electrode and touniformize the positional relationship between the cylindricalinsulating member and the discharge needles for every discharge needle.In this case incidentally, the ions generated in the cylindricalinsulator can be delivered out of the cylindrical insulator by supplyingair into the cylindrical insulator in the axial direction thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing an outline of an ion generator in afirst mode for implementing the present invention;

FIG. 2 is a circuit diagram of a high frequency AC high voltage powersource shown in FIG. 1;

FIG. 3 shows an external perspective view of an air nozzle type iongenerator in the first mode for implementation;

FIG. 4 illustrates the device shown in FIG. 3 along a longitudinalsection;

FIG. 5 is a circuit diagram showing an outline of an ion generator in asecond mode for implementing the invention;

FIG. 6 shows an external perspective view of an air blowing type iongenerator in the second mode for implementation;

FIG. 7 illustrates the device shown in FIG. 6 along a longitudinalsection;

FIG. 8 through FIG. 10 illustrate an electrode shown in FIG. 7;

FIG. 11 is a configuration diagram of a testing apparatus for the deviceshown in FIG. 6; and

FIG. 12 is a graph showing the performance of the device shown in FIG.6.

BEST MODES FOR CARRYING OUT THE INVENTION

A first mode for carrying out the present invention will be describedbelow with reference to FIG. 1 through FIG. 4.

Referring to FIG. 1, an ion generator 1 in the first mode for carryingout the invention comprises discharge needles 2, opposed electrodes 3opposite the discharge needles 2, a high frequency AC high voltage powersource 4 and condenser units (capacitance units) 5 as its electricalcircuit configuration.

Although two each of the discharge needles 2 and the opposed electrodes3 are shown in FIG. 1, at least one each could suffice. The number ofthe discharge needles 2 and that of the opposed electrodes 3 need not beequal, but one opposed electrode 3 may be disposed opposite a pluralityof discharge needles 2.

An output cable (high voltage output line) 4 a of the high frequency AChigh voltage power source 4 is connected to the discharge needles 2 viathe condenser units 5. The opposed electrodes 3 are connected to areturn cable 4 b of the high frequency AC high voltage power source 4,and the return cable 4 b is connected to the ground (grounded) via agrounding line 6. Therefore, the opposed electrodes 3 are grounded.

The condenser units 5 need not be condenser elements integrally formedas electronic parts, but may be members provided with insulators toserve as dielectrics (members structurally provided with requiredcapacitances). For instance, the condenser units 5 may be configured ofa single thin insulator, structures formed by connecting a metal memberand an insulating member, or structures formed by connecting metalmembers to both ends of an insulating member. In more general terms, thecondenser units 5 may be any structures which have required capacitiesand permit connection of the output cable 4 a and the discharge needles2.

The high frequency AC high voltage power source 4, as shown in FIG. 2,comprises an oscillator circuit 7 which generates a high frequency ACvoltage when a DC voltage is applied thereto, and a piezoelectrictransformer 9 which boosts the generated high frequency AC voltage witha piezoelectric element 8 consisting of a piezoelectric ceramic toobtain a high voltage. The oscillator circuit 7 is connected to a DCpower supply circuit 10 which generates a DC voltage from commercialpower 11, and a DC voltage is applied thereto from the DC power supplycircuit 10. The piezoelectric transformer 9 generates a high frequencyhigh voltage as the piezoelectric element 8 mechanically vibrates inresponse to the output of the oscillator circuit 7, and outputs the highfrequency high voltage from a terminal 12 to the output cable 4 a. Thefrequency of the high frequency high voltage outputted from thepiezoelectric transformer 9 is a high frequency in the range of 10 kHzto 100 kHz in this mode for implementation. Incidentally, with a view toprevent the vibration of the piezoelectric element 8 from generatingnoise, it is preferable for the frequency of the high frequency highvoltage outputted from the piezoelectric transformer 9 to be 20 kHz orabove.

To add, as the frequency of the high frequency high voltage outputtedfrom the piezoelectric transformer 9 is raised, the high frequencyhigh-voltage becomes lower. When its frequency is set to 100 kHz, themagnitude (amplitude) of the high frequency high voltage approaches thelimit of voltage at which the discharge needles 2 can generate a coronadischarge (about 1.8 kV). For this reason, the upper limit of thefrequency of the high frequency high voltage outputted from thepiezoelectric transformer 9 is set to 100 kHz in this mode forimplementation.

In the ion generator 1 of the above-described circuit configuration,when a high frequency high voltage is applied to the discharge needles 2by the high frequency AC high voltage power source 4, an electric fieldis formed between the discharge needles 2 and the opposed electrodes 3,and corona discharges are generated from the discharge needles 2 toenable positive and negative air ions to be generated.

Next, as a more specific embodiment of the ion generator 1 in the firstmode for implementation having the circuit configuration of FIG. 1, anair nozzle type ion generator 1 a will be described with reference toFIG. 3 and FIG. 4.

As shown in FIG. 3 and FIG. 4, the air nozzle type ion generator 1 acomprises a nozzle body 14 formed of an insulator, cylindrically shapedwith an air passage 13 penetrating inside thereof in the axial directionand one discharge needle 2 implanted therein, an opposed electrode 3disposed circularly along the outlet edge (one end of the nozzle body14) of the air passage 13, and a power source case 15 which, having thehigh frequency AC high voltage power source 4 built therein, is fixed onan external face (the under face in FIG. 3 and FIG. 4) of the nozzlebody 14.

An air feed pipe 16, connected to an air supply device not shown, isscrewed onto the inlet to the air passage 13 of the nozzle body 14. Ametal-made nozzle cap 18, at the tip of which an air outlet 17 isformed, is screwed onto the outlet of the air passage 13, so disposedthat the opposed electrode 3 is held between the nozzle cap 18 and thenozzle body 14. Therefore, the opposed electrodes 3 and the nozzle cap18 are in contact with each other to have electrical conductiontherebetween.

The air passage 13 in the nozzle body 14 is straight and has a roundcross-section from its inlet to outlet, but the air passage 13 b on theoutlet side, constituting the part from midway to the outlet, is madelarger in diameter than the air passage 13 a on the inlet side. And thecentral axis of the air passage 13 a on the inlet side is positionedabove the central axis of the air passage 13 b on the outlet side(closer to the side of the nozzle body 14 opposite to the power sourcecase 15) enlarged in diameter.

The discharge needle 2 is so screwed onto the nozzle body 14 via ametal-made socket 19 that its axis coincides with the central axis ofthe air passage 13 b and of the nozzle cap 18 and its tip is positionedat the center of the opposed electrode 3.

The output cable 4 a of the high frequency AC high voltage power source4 in the power source case 15 is covered with an insulative coveringmember 20 and, together with the insulative covering member 20, fixedinto a metal-made current collector ring 21. And the output cable 4 a,the insulative covering member 20 and the current collector ring 21 areinserted into the nozzle body 14 from the power source case 15 side inthe direction orthogonally crossing the axis of the discharge needle 2.The output cable 4 a, the insulative covering member 20 and the currentcollector ring 21 are so extended within the nozzle body 14 that theouter circumferential face of the current collector ring 21 comes intocontact (establishes electrical conduction) with the rear end of thedischarge needle 2 and the socket 19 fitted to the rear end thereof. Theinsulative cover 20 and the current collector ring 21 here constitutethe condenser unit 5 in FIG. 1. Namely, the insulative cover 20 as theinsulator is placed intervening between the output cable 4 a of the highfrequency AC high voltage power source 4 and the discharge needle 2. Inother words, when the output cable 4 a which is a conductor serving asthe core wire is provided with the insulative cover 20 consisting of aninsulator, and establishing conduction from the outer circumferentialface of the current collector ring 21 which covers the outside thereofand consists of a conductor to discharge needle 2, the discharge needle2 is capacitance-coupled with the output cable 4 a by the currentcollector ring 21 and the insulative covering member 20.

Also, the return cable 4 b of the high frequency AC high voltage powersource 4 is directly connected from the power source case 15 to theopposed electrode 3 to be in conduction with the opposed electrode 3.The opposed electrode 3, as described, is in contact and conduction withthe nozzle cap 18. The nozzle cap 18, as it is metal-made and inconduction with the opposed electrode 3, can function, together with theopposed electrode 3 to which the return cable 4 b is connected, as anelectrode opposite the discharge needle 2. Thus, corona discharging ismade possible between the discharge needle 2 and the nozzle cap 18.

In the nozzle type ion generator 1 a of the configuration describedabove, when a high voltage (about 2 kV) of a high frequency of 10 to 100kHz is applied to the discharge needle 2 by the high frequency AC highvoltage power source 4, an electric field is formed between thedischarge needles 2 and the nozzle cap 18. Then the electric fieldconcentrates on the tip of the discharge needle 2 to generate a coronadischarge to give rise to positive and negative air ions. Also, air issupplied from an air supply device not shown to around the dischargeneedle 2 via the air feed pipe 16 and the air passage 13. Since the airions generated in the space in the tip part of the discharge needle 2are transferred as a result, air containing the air ions is ejected fromthe ion outlet 17. And the static electricity of a charged objectpositioned in front of the ion outlet 17 can be neutralized (removed).

In the first mode for implementation described above, the dischargeneedle 2 for generating air ions is capacitance-coupled with the outputcable 4 a of the high frequency AC high voltage power source 4. As aresult, the quantities of positive and negative air ions in the spacenear the tip of the discharge needle 2 can be substantially equalizedthereby to keep a good ion balance between the positive and negative airions. The following reason is conceivable for this result.

When the quantity of negative air ions is greater than that of positiveair ions in the space near the tip of the discharge needle 2, positiveair ions remain in the discharge needles 2 because the condenser unit 5intervenes between the discharge needles 2 and the output cable 4 a ofthe high frequency AC high voltage power source 4 to bring the potentialof the discharge needle 2 toward the positive side. For this reason,when a positive voltage is applied to the discharge needle 2, thepotential difference between the discharge needle 2 and the opposedelectrode 3 widens, and the generated quantity of positive air ionsincreases. Conversely, when a negative voltage is applied to thedischarge needles 2, the potential difference between the dischargeneedle 2 and the opposed electrode 3 narrows, and the generated quantityof negative air ions decreases. Conceivably as a result of thesephenomena, the quantities of positive and negative air ions in the spacenear the tip of the discharge needle 2 are substantially equalized. Andeven if there are more positive air ions than negative air ions in thespace near the tip of the discharge needle 2, the same process as whatwas described above is likely to make adjustment to eliminate theunevenness of the quantities of positive and negative air ions.

Also, the condenser unit 5 can be configured to have such a capacitanceas will make the voltage drop (the voltage drop in the condenser unit 5)at the time of corona discharging to be sufficiently small (acapacitance that allows the discharge needle 2 to generate a coronadischarge without any trouble).

For instance, the diameter of the output cable 4 a is set to 2 mm, thethickness of the insulative covering member 20 to 1 mm, the bore of thecurrent collector ring 21 to 4 mm and the length of the currentcollector ring 21 to 20 mm. Further, the specific inductive capacity ofthe insulative covering member 20 is set to 5.0. In this case, thecapacitance of the condenser units 5 will be about 8.4 pF, and itsimpedance is between about 2 MΩ and 0.2 MΩ in the range of 10 kHz to 100kHz. And since the discharge amperage of one discharge needle 2 at thetime of corona discharging is about 3 μA to 10 μA , the voltage drop inthe condenser unit 5 can be restrained to 2 V or less at any frequencyin the range of 10 kHz to 100 kHz. And, since this voltage drop issufficiently smaller than the output voltage that can be generated bythe high frequency AC high voltage power source 4 (2 to 3 kV), a voltagenot lower than the voltage needed for corona discharging (a voltage ofabout 1.8 kV in amplitude) can be applied to the discharge needle 2without any trouble.

Also, since the current that can be outputted by the piezoelectrictransformer 9 is at most 100 μA, the short-circuiting current thatoccurs when something comes into contact with the discharge needle 2 canbe kept sufficiently small irrespective of the capacitance of thecondenser unit 5.

Also, even if a drift or the like occurs in the high frequency AC highvoltage power source 4 and a DC component is contained in the highvoltage current supplied from the high frequency AC high voltage powersource 4 to the discharge needle 2, it can be cut by the condenser unit5. For this reason, it is possible to provide an ion generator which cansecure the stability of the ion balance and excels in deelectrifyingcapability.

To add, though a nozzle type ion generator to which air is fed fromoutside via the air feed pipe 16 was described above as an example ofthis mode for implementation, an air blowing type device in whichgenerated air ions are transferred by a fan can give the same effect ifthe configuration of the electrical circuit shown in FIG. 1 and FIG. 2is the same.

Next will be described an ion generator in a second mode forimplementing the present invention with reference to FIG. 5. An iongenerator 1 b in the second mode for implementation, as shown in FIG. 5,has the same circuit configuration as the ion generator 1 in the firstmode for implementation except for condenser units 5 b (capacitanceunits). Therefore, the same constituent parts as in the ion generator 1will be assigned respectively the same reference numerals, and theirdescription will be dispensed with.

The condenser units 5 b are connected to the opposed electrodes 3 in astate of being opposed to the discharge needles 2. Therefore, thecurrent at the time of corona discharging between the discharge needles2 and the opposed electrodes 3 flows via the condenser units 5 b. Thesecondenser units 5 b need not be condenser elements integrally formed aselectronic parts, as in the case of the condenser unit 5, but may aswell be members provided with insulators to serve as dielectrics (forinstance, the same structures as the condenser units 5).

The ion generator 1 b of the circuit configuration described above cangenerate positive and negative air ions when a high frequency highvoltage is applied by the high frequency AC high voltage power source 4to the discharge needles 2 as corona discharging takes place between thedischarge needles 2 and the opposed electrodes 3 via the condenser units5 b.

Next will be described with reference to FIG. 6 through FIG. 10 an airblowing type ion generator 1 c as a more specific embodiment of the iongenerator 1 b in the second mode for implementation, having the circuitconfiguration shown in FIG. 5.

Referring to FIG. 6 through FIG. 10, the air blowing type ion generator1 c in the second mode for implementation comprises a case 33 having anair outlet 31 opened in its front face and an air inlet 32 in its rearface. The case 33 is made of metal for instance, but may as well becomposed of an insulator. On the front face of the case 33 a louver 34covering the outlet 31 and a power switch 35 are disposed, and on therear face of the case 33 a filter set 36 covering the air inlet 32 isprovided. And air is sucked in through the filter set 36, and aircontaining air ions generated within the case 33 are blown out throughthe louver 34. Incidentally, the louver 34 and the filter set 36 areconfigured to be detachable from the case 33. In FIG. 7, illustration ofthe louver 34 is dispensed with.

Within the case 33, blower means 37 and ion generator means 38 arearranged in that order from rear to front. The blower means 37, composedof a cylindrical fan housing 39 fixed to the air inlet 32 and a fan 40housed in the fan housing 39 and driven by a motor not shown, blows airby the rotational driving of the fan 40 from the air inlet 32 toward theair outlet 31.

The ion generator means 38 comprises an air guide cylinder 41(cylindrical insulator) consisting of an insulator and disposed incontinuity to the front of the fan housing 39, the opposed electrodes 3consisting of annular conductors fitted to the outer circumference ofthe air guide cylinder 41, a plurality of (eight in this mode forimplementation) discharge needles 2 radially arranged within the airguide cylinder 41, spaced from one another around the axis of theopposed electrodes 3 (the axis of the air guide cylinder 41), and anelectrode holder 42 for holding the base ends of these discharge needles2. The axes of the opposed electrodes 3 and the air guide cylinder 41coincide with the axis of rotation of the fan 40.

The electrode holder 42, arranged in the central part of the air ionguide cylinder 41, comprises a round substrate 44 (plate-shapedinsulator) formed of an insulator, whose rear face is supported andfixed by the air ion guide cylinder 41 via a supporting member 43, eightmetal-made (electroconductive) sockets 19 c radially arranged in a fixedmanner on the front face of the substrate 44 matching the arrangement ofthe discharge needles 2, and a circuit pattern 45 (pattern of anelectroconductive thin film layer) formed on the rear face of thesubstrate 44 in a pattern matching the arrangement of the sockets 19 c.The eight sockets 19 c correspond to the first conductor pattern in thecontext of the present invention, while the circuit pattern 45corresponds to the second conductor pattern in the context of theinvention. The sockets 19 c correspond to the partial conductorconstituting the first conductor pattern. Incidentally, the substrate 44may have circuit patterns formed on the two faces.

The substrate 44, with its central axis (the axis in the normaldirection) kept coinciding with the axes of the opposed electrodes 3 andof the air guide cylinder 41, is disposed in the central part of the airguide cylinder 41.

The eight sockets 19 c, as shown in FIG. 9, are fixed on the front faceof the substrate 44 in a state in which they are insulated from oneanother by the substrate 44.

The circuit pattern 45, as shown in FIG. 10, comprises an annularportion 45 a surrounding the central area of the rear face of thesubstrate 44 fixed to the supporting member 43, eight radial portions 45b in conduction with the annular portion 45 a radially arrayed andformed in parts of the rear face of the substrate 44 and matching thesockets 19 c (parts opposite the sockets 19 c in the direction of thethickness of the substrate 44), and a cable connecting part 45 c inconduction with the annular portion 45 a between the adjoining radialportions 45 b and 45 b. The radial portions 45 b are in conduction withone another via the annular portion 45 a. Incidentally, the annularportion 45 a and the radial portions 45 b correspond to the partialconductors of the second conductor pattern in the context of theinvention.

And as shown in FIG. 7, the output cable 4 a of the high frequency AChigh voltage power source 4 arranged on the inner bottom region of thecase 33 is connected to the cable connecting part 45 c of the circuitpattern 45. The base of each discharge needle 2 is inserted into andfixed in each socket 19 c of the electrode holder 42 with the axis ofthe discharge needle 2 oriented to the radial direction of the substrate44. Here, the sockets 19 c, the substrate 44 and the circuit pattern 45constitute the condenser units 5 shown in FIG. 5. The condenser units 5in this case, with the sockets 19 c and the circuit pattern 45 servingas electrodes, have functions of parallel plate condensers using thesubstrate 44 intervening between these electrodes as a dielectric. Inmore detail, the parallel plate condenser is formed with the sockets 19c and the radial portions 45 b of the circuit pattern 45 opposingthereto serving as electrodes and the substrate 44 between theseelectrodes as a dielectric. In other words, the discharge needles 2 arecapacitance-coupled with the output cable 4 a of the high frequency AChigh voltage power source 4 by the sockets 19 c fixing them and thesubstrate 44 which is an insulator between the sockets 19 c and theradial portions 45 b opposite them.

Also, the return cable 4 b of the high frequency AC high voltage powersource 4 is connected to (in conduction with) the opposed electrodes 3.Since the opposed electrodes 3 here are fitted to the outercircumference of the air guide cylinder 41 formed of an insulator, thesurfaces of the opposed electrodes 3 opposite the discharge needles 2are covered by an insulator (the air guide cylinder 41). Also, as theair guide cylinder 41 is connected to the opposed electrodes 3 oppositethe tips of the discharge needles 2, the guide cylinder 41 constitutesthe condenser units 5 b of FIG. 5.

In the air blowing type ion generator 1 c of the above-describedconfiguration, when a high voltage (about 2 kV) of a high frequency of10 to 100 kHz is applied by the high frequency AC high voltage powersource 4 to the discharge needles 2, corona discharging takes placebetween the discharge needles 2 and the opposed electrodes 3 via the airguide cylinder 41 to generate positive and negative air ions. And whenair is blown by the rotational driving of the fan 40 from the air inlet32 to the air outlet 31, the air sucked via the filter set 36 is guidedby the air guide cylinder 41 to be supplied to the vicinity of thedischarge needles 2. Since the air ions then generated in the space nearthe tip part of the discharge needle 2 is transferred to the front sideof the case 33, air containing the air ions is supplied through thelouver 34. And the static electricity of a charged object positioned ina remote position can be neutralized and removed.

In the second mode for implementation described above, not only the sameeffect as in the first mode for implementation can be achieved but also,as the condenser units 5 b are provided, the ion balance betweenpositive and negative air ions (in more detail, the balance betweenpositive and negative air ions which are transferred to the front sideof the case 33 without being captured by the air guide cylinder 41 oranything else) is further improved. The conceivable reason for this isas follows.

Thus, even if the positive and negative air ions generated in the spacenear the tip region of the discharge needles 2 are balanced in equalquantities, if the quantities of positive and negative ions directedtoward the opposed electrodes 3 differ, the balance between thequantities of positive and negative ions supplied to the outside of thecase 33 may be lost. However, since the condenser units 5 b are providedin this mode for implementation, if positive air ions directed to theopposed electrodes 3 increase, the potential on the inner circumferenceof the air guide cylinder 41 which constitutes the condenser units 5 bfitted with the opposed electrodes 3 becomes more dominantly positive.For this reason, when a positive voltage is applied to the dischargeneedles 2, the difference in potential between the discharge needles 2and the inner circumference of the air guide cylinder 41 becomessmaller, and the quantity of positive air ions generated decreases. As aresult, the quantity of positive air ions supplied to the outside of thecase 33 decreases. Conversely, when negative air ions directed to theopposed electrodes 3 increase, the potential on the inner circumferenceof the air guide cylinder 41 becomes more dominantly negative. For thisreason, when a negative voltage is applied to the discharge needles 2,the difference in potential between the discharge needles 2 and theinner circumference of the air guide cylinder 41 becomes smaller, andthe quantity of negative air ions generated decreases. As a result, thequantity of positive ions supplied to the outside of the case 33decreases. This conceivably causes the quantities of the positive andnegative air ions directed to the opposed electrodes 3 to be balanced,resulting in balancing of the quantities of positive and negative ionssupplied to outside the case 33 as well.

To add, the condenser units 5 in this mode for implementation canobviously be configured to have such capacitances as will make thevoltage drop (the voltage drop in the condenser units 5) at the time ofcorona discharging to be sufficiently small, and an example of thisconfiguration will be shown below.

If, for instance, a phenol resin-made substrate (about 5 in specificinductive capacity) of 1 mm in thickness is used as the substrate 44,and to set the area of each radial portion 45 b of the circuit pattern45 to be 113×10⁻⁶ m² for example. The capacitance of the condenser unit5 for each discharge needle 2 then will be about 5 pF. The impedance ofthe condenser unit 5 is about 3 MΩ to 0.3 MΩ in the range of 10 kHz to100 kHz. And since the discharge amperage of one discharge needle 2 atthe time of corona discharging is about 3 μA to 10 μA, the voltage dropin the condenser unit 5 can be restrained to 3V or less at any frequencyin the range of 10 kHz to 100 kHz. As this voltage drop is sufficientlysmaller than the output voltage that can be generated by the highfrequency AC high voltage power source 4 (2 to 3 kV), a voltage notlower than the voltage needed for corona discharging (a voltage of about1.8 kV in amplitude) can be applied to the discharge needle 2 withoutany trouble.

To add, though an air blowing type ion generator was described above asan example of the second mode for implementation, a nozzle type devicelike the one described above with reference to the first mode forimplementation can give the same effect if the configuration of theelectrical circuit is the same as what is shown in FIG. 5.

Ion generators according to the invention are not limited to the devicesreferred to in describing the first and second modes for implementationabove, but the material, shape and size for configuration of thecondenser units 5 or 5 b can be appropriately selected otherwise. Inthis case, in order to cause the discharge needles 2 to accomplishcorona discharging, a voltage of not less than about 1.8 kV has to beprovided to the discharge needles 2. Also since, the output voltage ofthe high frequency AC high-voltage power source 4 (the voltage generatedon the output cable 4 a) is about 2 to 3 kV, it is preferable for thevoltage between the output cable 4 a and the discharge needles 2 at thetime of corona discharging to be kept at no higher than about 100 V atthe maximum. And since the discharge amperage at the time of coronadischarging is about 3 to 10 μA, in order to keep the voltage drop ofthe condenser units 5 at about 100 V, the impedance of the condenserunits 5 has to be kept at no more than 10 MΩ at the maximum. Therefore,it is desirable for the capacitances of the condenser units 5 to be soset as to keep the impedance at no more than 10 MΩ at a frequency of 10to 100 kHz. Such capacitances can be realized with no trouble by thestructure of the condenser units 5 described above with reference to thefirst and second modes for implementation. For instance, thecapacitances may be from 0.1 to 10 pF approximately. To add, the greaterthe capacitances of the condenser units 5, the greater the areas of thecondenser units 5 (the areas contributing to the capacitances) will haveto be. Accordingly, considering the dimensions of the condenser units 5,it is desirable for the capacitances of the condenser units 5 to be nomore than about 10 pF at the maximum for practical purposes.

With respect to a case in which the condenser units 5 of the air blowingtype ion generator 1 c in the second mode for implementation describedabove has a preferable level of static capacitances, the performance ofthe device will be described. Referring to FIG. 11, the inventorspertaining to the present application conducted a test to check thedeelectrifying effect of this air blowing type ion generator 1 c byusing a charged plate monitor 50. The charge plate monitor 50 comprisesa metal plate 53 fitted to its body 52 via an insulating member 51, andhas within the body 52 a surface potential measuring device 54 formeasuring the potential of the metal plate 53, a high-voltage powersource 55 for providing an electric charge to the metal plate 53, and atimer 56 for measuring the varying time of the potential of the metalplate 53.

First, the metal plate 53 of 150 mm square was arranged in a position ata distance of 300 mm from the air blowing type ion generator 1 c(Example). And the metal plate 53 was charged with +1000 V (or −1000 V)by the high voltage power source 55.

First, an AC voltage of 68 kHz, 2 kV (0−p) was applied to the dischargeneedles 2 by the high frequency AC high voltage power source 4 of theair blowing type ion generator 1 c to cause positive and negative airions to be generated by corona discharging, and the generated air ionswere supplied from the air blowing type ion generator 1 c to the metalplate 53. And the charge of the metal plate 53 was neutralized by thesupply, and the length of time taken by the potential of the metal plate53 to attenuate from the initial voltage of +1000 V (or −1000 V) to +100V (or −100 V) was measured as the attenuation time. The result ofmeasurement is shown in Table 1. To add, when the ion generator ofComparative Example for comparison with Example was used, theattenuation time was measured in the same way as described above. Thedevice of Comparative Example used for the measurement is an air blowingtype device provided with the high frequency AC high voltage powersource 4 and has the same configuration as the air blowing type iongenerator 1 c except that it uses directly connected type electrodes ofa structure in which the discharge needles 2 and the output cable 4 aare directly connected (provided with the air guide cylinder 41 forcovering the opposed electrodes 3). The result of measuring thisComparative Example is shown in Table 1 together with that of Example.

TABLE 1 Comparative Example Example Attenuation time +1000 → +100 (sec)1.8 1.9 Attenuation time −1000 → −100 (sec) 1.9 2.0 Offset voltage (V)+1 to +2 −2 to +10

Next, with the metal plate 53 being used as the charged object, aircontaining air ions was continuously blown on the metal plate 53 of thecharged plate monitor 50 from the air blowing type ion generator 1 c. Inthis procedure, the voltage attributable to the charge accumulated onthe metal plate 53 was consecutively measured as the offset voltage withthe surface potential measuring device 54. The offset voltage serves asthe indicator of the balance between the quantities of positive andnegative air ions (ion balance) discharged from the air blowing type iongenerator 1 c to the metal plate 53. As the absolute value of the offsetvoltage increases when the quantities of positive and negative air ionsdischarged from the air blowing type ion generator 1 c are uneven, asmaller absolute value of the voltage indicates a correspondingly goodion balance. To add, where the device of the aforementioned ComparativeExample was used, the offset voltage was measured in the same way asdescribed above.

The result of measurement of this offset voltage is shown in Table 1cited above and FIG. 12. In FIG. 12, the vertical axis represents theoperating duration [h] of the air blowing type ion generator and thehorizontal axis represents the offset voltage [V], FIG. 12( a) shows thetest result of Example and FIG. 12( b) shows the test result ofComparative Example.

As referencing Table 1 would make it evident, though the attenuationtime is substantially equal between the Example and the ComparativeExample, the margin of variation of the offset voltage is found farsmaller in the Example than in the Comparative Example. Moreover, theoffset voltage in the Example is kept to a voltage substantially closeto 0. Further, the variations in offset voltage over time, as shown inFIG. 12, are evidently more stable in the Example than in theComparative Example. Therefore, the ion balance of positive and negativeair ions discharged from the ion generator 1 c toward the metal plate 53is evidently better than in the device of Comparative Example.

INDUSTRIAL APPLICATION

As hitherto described, the ion generator according to the presentinvention is useful as what can so generate positive and negative airions that various charged objects can be effectively deelectrified, andsuitable for deelectrifying charged objects, such as semiconductordevices, which require a high deelectrifying effect.

1. An ion generator, comprising at least one discharge needle, anopposed electrode opposite the discharge needle, and an AC high voltagepower source for applying a high voltage between the discharge needleand the opposed electrode, for generating positive and negative air ionsby giving rise to a corona discharge when a high voltage is appliedbetween the discharge needle and the opposed electrode by the AC highvoltage power source, wherein the AC high voltage power source comprisesa high frequency oscillator and a piezoelectric transformer, and outputsa high frequency voltage, and an insulator is placed intervening betweenthe high voltage output line of said AC high voltage power source andthe discharge needle, thereby establishing a capacitive coupling betweensaid AC high voltage power source and said discharge needle, to enablethe discharge needle to accomplish discharging.
 2. The ion generatoraccording to claim 1, wherein the high voltage output line of said AChigh voltage power source is covered with an insulating tube as saidinsulator, the high voltage output line covered with this insulatingtube is inserted into a current collector ring formed of a conductor ina state in which the high voltage output line is insulated from thecurrent collector ring by the insulating tube, and conduction isestablished between the surface of the current collector ring into whichthe high voltage output line is inserted and said discharge needle. 3.The ion generator according to claim 1, wherein conduction of saiddischarge needle is established with a first conductor pattern formed onone face of the plate-shaped insulator as said insulator, and conductionof said high voltage output line is established with a second conductorpattern formed on the other face of the plate-shaped insulator in aposition matching the first conductor pattern.
 4. The ion generatoraccording to claim 3, wherein a plurality of said discharge needles areprovided, said first conductor pattern comprises a plurality of partialconductors establishing conduction of the discharge needles with oneanother arranged on one face of the plate-shaped insulator in a patternin which the partial conductors are insulated from one another by saidplate-shaped insulator and matched with the arrangement of the pluralityof discharge needles, and said second conductor pattern comprises aplurality of partial conductors opposite the partial conductors of thefirst conductor pattern via the plate-shaped insulator and a partialconductor linking this plurality of partial conductors in conductionwith one another.
 5. The ion generator according to claim 4, wherein aplurality of the discharge needles, with the base end of each beingfixed to the partial conductors of the first conductor pattern on theplate-shaped insulator 1, are laid extending around the plate-shapedinsulator in a pattern of arrangement radiating from the plate-shapedinsulator, and said opposed electrode is composed of an annularconductor so arranged around the plurality of discharge needles as tohave an axis in a direction substantially orthogonal to the axis of eachdischarge needle.
 6. The ion generator according to claim 1, wherein thesurface of said opposed electrode facing the discharge needles iscovered with an insulator.
 7. The ion generator according to claim 5,wherein the opposed electrode which is said annular conductor is fittedto the outer circumference of a cylindrical insulator, the cylindricalinsulator accommodating therein a plurality of the discharge needles andthe plate-shaped insulator and being arranged coaxially with the annularconductor, and comprises, within the cylindrical insulator, means ofsupplying air in the axial direction thereof.
 8. The ion generatoraccording to claim 2, wherein the surface of said opposed electrodefacing the discharge needles is covered with an insulator.
 9. The iongenerator according to claim 3, wherein the surface of said opposedelectrode facing the discharge needles is covered with an insulator. 10.The ion generator according to claim 4, wherein the surface of saidopposed electrode facing the discharge needles is covered with aninsulator.
 11. The ion generator according to claim 5, wherein thesurface of said opposed electrode facing the discharge needles iscovered with an insulator.